Digital distribution of data, e.g. multimedia content, has been gaining more and more attention over the recent years. In this respect, it is known to distribute data on the basis of a descriptive file, also referred to as a metafile. Examples of such descriptive files are, e.g. a torrent file as used according to the BitTorrent protocol and a playlist file as used according to the HTTP Live streaming protocol. Typically, a recipient of the data will use information in the descriptive file as a basis for obtaining the data. Such information may be identifiers uniquely associated with pieces of the data to be received. Actual reception of the data may then occur from different sources, e.g. according to a peer-to-peer (P2P) protocol. One example of a P2P protocol is the above-mentioned BitTorrent protocol.
In P2P protocols, content is shared among all users that are part of a P2P network. For this purpose, a descriptive file exists for every content item available in the network. In this respect, “available” means that at least one member of the network, also referred to as a “peer”, is offering this content item. In the descriptive file, small pieces of the content item are addressed. When a user requests a certain content item, these pieces may be served from different members of the network. This has the advantage that the recipient of the content item does not have to rely on certain peers providing the pieces to be online the whole time until the content item is received completely. Every piece may be served from the most suitable location, e.g. from a location to which there is a data connection with low latency and high bit rate.
According to known P2P techniques, the descriptive file of a content item contains hash values of the different pieces. The individual hash values of the different pieces are used to identify the pieces upon reception. Further, the descriptive file includes a hash value obtained on the basis of these individual hash values. The latter hash value may be used as a signature to uniquely identify the content item and to verify the integrity of the descriptive file. Hence, when modifying one piece of the content item, the corresponding individual hash value and also the hash value computed on the basis of the individual hash values will change. Accordingly, even though only one piece of the content item has been modified, the hash value computed from the individual hash values will be interpreted as referring to a different content item. For example, a content item in the form of a movie with advertisements for young boys would have a different signature than the same movie with advertisements for middle-aged women. The consequences are that each individualized version of the movie would be considered as totally distinct content which needs a distinct storage. In other words, even the pieces of the content item which are the same in both individualized versions would need to be provided separately.
Accordingly, there is a need for techniques which allow for efficiently communicating individualized data to different recipients.